In the art of back water check valves for installation in a sanitary sewer line, for example, as disclosed in U.S. Pat. Nos. 1,991,081, No. 2;904,064 and No. 4,637,425, various designs have been proposed or used for automatically closing a valve member in the event that sewage water backs tip within the drain line. This prevents the sewage water from backing up into the building.
As disclosed in Pat. No. 1,991,081, a float member is used to sense the water level within the drain line, and the float member operates a controller for controlling a reversible motor which opens and closes a gate valve. In Pat. No. 2,904,064, a back water valve includes a gate valve member which is spring loaded in an open position, and a float senses the elevated water within the drain line and releases or trips the gate valve member for closing in the event the float is elevated by water backing up in the drain line. Pat. No. 4,637,425 discloses a flapper-type check valve which has a pivoting valve member. The valve member is pivoted to a closed position by a spring actuated rod which is released from its cocked position by actuation of a solenoid controlled by a float actuated switch. After the backed up water drains from the sewer line, the check valves are manually reset. Other types of fluid actuated gate valves have also been constructed or proposed, for example, as disclosed in U.S. Pat. No. 1,685,932.
In any such back water valve for use in a sanitary sewer line extending from a building, it is desirable for the valve to be simple and economical in construction, be dependable and reliable in operation, be easy to assemble and install, avoid any flow restriction in the drain line when valve is open, and be automatic in operation. That is, it is desirable for the valve to close positively when water backs up in the sewer line and then automatically open when the sewer line is again open for use. After analyzing the back water valves or check valves disclosed in the above patents, it is apparent that none of the valves provide all of the desirable features mentioned above.